Radio transmitting system



May 22, 1928.

T. L. ECKERSLEY RADIO TRANSMITTING SYSTEM Filed June 11, 1924 INVENTOR THOMAS L. ECKERSLEY RNEY Patented May 22, 1928.

UNITED STATES PATENT OFFICE.

'lHOMAS LYDWELL ECKERSLEY, OF DANBURY, ENGLAND, ASSIGNOR TO RADIO COR- PORATION OF AMERICA, A CORPORATION OF DELAWARE.

zanmo TRANSMITTING SY$TEM.

Application filed June 11, 1824, Serial No. 719,246, and in Great Britain .Tune 27, 1923. 1

Filter circuits, chains of inductances and capacities have been extensively used in receiving and telephonecircuits for the purpose of eliminating undesired frequencies, but have not yet been successfully applied in transmitting valve circuits to cut out the undesirable harmonics which are. radiated When the set is working efficiently. v

This failure is dueto the fact that when the filter is placed between the valve set and the aerial in the feed circuitof the former,oscillationsof the natural period of the filter circuit are set up, owing to the presence of capacity reaction in the valves and other spurious reaction which cannot usually be eliminated. r

Even when it is possible, by careful balancing to eliminate these spurious oscillations, the arrangement is inefficient, ,on account of the high impedance of the feed circuit to the high frequency harmonics.

According to this invention, these .difiiculties are obviated by the use between the anode ieedcircuit and the filter 'circuit of a closed oscillatory circuit tuned tothe fundamental frequency. The filter circuit is shunted across a suitablefraetion of the inductance of the closed circuit, or is coupled thereto. r q l o The tuned circuit acts as a filter roe any oscillations in the filter circuit, the frequency of which differs from that ofthe tuned circuit and thereforethe potentials applied by these oscillations to the plate of the valve, and by capacity reaction .to the grid are relatively small. and the tendency to self oscillation is reduced to a minimum.

Keying with suchan arrangement is preferably effected by arranging a resistance in parallel with the aerial tuning inductance and alternately connecting one of the end terminals of the filter circuit to the resistance and to the inductance, By suitably adjusting the value of the resistance, the load on the valve may thus be kept constant.

My invention is illustrated by the accompanying drawing, in which Figs. 1 and 2 are dia 'rammatic representations of circuits embodying the invention. In each of the figures corresponding parts are indicated by the same reference characters. I

In the drawings 1 is the main oscillating valve and 2 is the inductance in the anode circuit thereof.

In Fig. 1 L, C is the closed circuit tuned to the transmitting wave length. This circuit is closely coupled to the inductance 2, and also to an inductance 3 across one end of a filter circuit, the other end of which is formed of an inductance i coupled to the aerial 5. i

A. similar arrangement is shown in Fig. 2 but in this modification the input and output of the filter are direct coupled to inductances L1 and 5 respectively. a

The filter circuit illustrated, consists of a series of inductances 6 and shunt condensers 7. The first and last of the inductances 6 are of a value half that of the intermediate inductances.

The conditions which determine the value of each of the intermediate inductances and of the condensers, are that p LG=2 Where p=21r frequency, and that'the ratio of the voltage across the filter to current through the filter should be equal to This choice of constants ensures that (1) the amplitude oflthe fundamental frequency n is unchanged in transmission along the filter,

and (2) all harmonics are reduced to a small amplitude which depends on the number of stages of the filter. l i

, The coils 3'and 4 should be provided with alarge number of adjustable tappings. The

tappingonthc coil 4: should be such that the impedance oft-he filter should be as above stated. The tapping on the coil?) determines the ratio of the current in the circuit L C This ratio, should not i to that in the aerial. be made too small, otherwise the diiiiculty of avoiding the natural oscillations of the filter circuit will reappear.

Other forms of filter circuit may obviously be employed. Thus, the end. inductance dmay be omitted and each of the end condensers may have a capacity twice that of each of the intermediate condensers.

Or, the intermediate inductances may be pressed by generated is passed and the harmonics suppressed by said filter circuit, of a closed oscillatory circuit tuned to the fundamental frequency and interposed between the valve generator and the filter circuit.

2 In a transmitting system the combination with a valve generator, an anode circuit therefor, a filter circuit consisting of a plurality of series inductances with parallel capacities therebetween whereby the fundamental frequency generated is passed and the harmonics suppressed by said filter circuit, an oscillatory link circuit external to the generator tuned to the fundamental frequency coupled to the anode circuit of said generator and the filter circuit.

3. In a transmitting system, the combination with an aerial circuit a valve generator, an output circuit therefor, a filter circuit consisting of a plurality of series inductances with parallel capacities therebetween whereby the fundamental frequency generated is passed and the harmonics suppressed by said filter circuit between the valve output and the aerial circuit, and a circuittuned to the fundamental frequency generated, and external to the generator interposed between the output of the valve and the filter.

4. In a transmitting system, the combination with a valve generator and a filter circuit consistingof a plurality of series inductances with parallel capacities therebetween whereby the fundamental frequency generated is passed and the harmonics supsaid filter circuit, an oscillatory circuit external to the generator tuned to the fundamental frequency generated and inductively coupled to the filter and the output of the valve.

5. In a transmitting system, the combination with a valve generator and a. filter circuit consisting of a plurality of series inductances with parallel capacities therebetween whereby the fundamental frequency generated is passed and the harmonics suppressed by said filter circuit, of an oscillatory circuit tuned to the fundamental frequency conductively coupled to the inductance of the filter and inductively coupled to the output of the'valve.

6. In a transmitting system a valve generator, an output circuit therefore, a variable inductance for said output circuit, a filter circuit associated with said output circuit and an oscillatory link circuit external to said generator coupled to said output circuit and to said filter circuit and tuned to the frequency to be transmitted whereby all oscillations set up in the filter circuit except those at the fundamental frequency are prevented from reacting on said generator.

7. In a transmitting system a valve generator, a filter circuit consisting of a series of inductances and parallel capacities therebetween, the end inductances of said series being of a value half that of the intermediate inductances, said intermediate inductances and condensers being so chosen that LG (I+21r f coupled to said generator, and an oscillatory circuit tuned to the fundamental frequency and coupled to said generator and said filter circuit.

8. In a transmitting system a valve generatora filter circuit consisting of a series of inductances and parallel capacities therebetween, the inductances and capacities of said filter being so chosen that the ratio of the voltage across the filter to the current through the filter is equal to a'fI; coupled to said generator, and an oscillating circuit tuned to the fundamental. frequency and coupled to said generator and said filter.

THOMAS LYDWELL ECKERSLEY.

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